Polyacene compounds including pentacene have now received attention as organic electronic materials for organic semiconductors or organic electroconductive materials, etc. However, it is not easy to introduce a substituent of any type at any position of the side chain on the polyacene skeleton, and hence there has been a demand for achieving simpler production of a desired compound.
For introduction of substituents at the 6- and 13-positions of the pentacene skeleton, the method of Maulding et al. has been known (Non-patent Document 1: D. R. Maulding, and Bernard G Roberts “Electronic absorption and fluorescence of phenylethynyl-substituted acenes” J. Org. Chem., 34, 1969, pp 1734). In the method of Maulding et al., pentacenequinone is reacted with Grignard reagents to thereby introduce substituted alkynylene groups at the 6- and 13-positions of the pentacene skeleton (see the scheme shown below).

Moreover, for synthesis of a pentacene derivative using pentacenequinone as a starting compound, the method of Miller et al. has also been known (Non-patent Document 2: Kaur, W. Jia, R. P. Kopreski, S. Selvarasah, M. R. Dokmeci, C. Pramanik, N. E. McGruer, G P. Miller “Substituent Effects in Pentacenes: Gaining Control over HOMO-LUMO Gaps and Photooxidative Resistances” J. Am. Chem. Soc., 130, 2008, pp 16274). In the method of Miller et al., pentacenequinone is reduced to convert its 6- and 13-positions into hydroxy groups, which are then replaced with alkylthiol groups, finally followed by aromatization with chloranil to thereby introduce alkylthio groups (see the scheme shown below).

However, these conventional methods have problems in that desired compounds cannot be obtained in high yields or are difficult to isolate because side reactions may occur in these methods.
For example, during reaction between pentacenequinone and thienyl groups, there is a risk that substituents on the thienyl groups will cause a reaction by which two thienyl groups are transferred to the same side during diol formation (Non-patent Document 3: N. Vets, M. Smet, W. Dehaen, “Reduction versus Rearrangement of 6,13-Dihydro-6,13-diarylpentacene-6,13-diols Affording 6,13- and 13,13-Substituted Pentacene Derivatives, Substituted Nephtacaenes and Pentacenes” SYNLETT 2005, pp 0217).
Moreover, during reaction between pentacenequinone and phenyl Grignard, 1,4-addition reaction will occur that does not target the carbonyls at the 6- and 13-positions of pentacene, but attacks their adjacent rings, so that a phenyl group is attached to the second ring (Non-patent Document 4: C. F. H. Allen, A. Bell “Action of Grignard Reagents on Certain Pentacenequinones, 6,13-Diphenylpentacene” J. Am. Chem. Soc., 64, 1942 pp 1253).
Furthermore, it is well known that upon reaction with alkyllithium or alkyl Grignard reagents in an attempt to introduce alkyl groups at the 6- and 13-positions of pentacene, isomerization reaction will occur and desired compounds cannot be obtained at all. In this conventional method starting with pentacenequinone, nobody has succeeded in introducing alkyl groups.
In contrast, the inventors of the present invention have proposed a new approach to form the pentacene skeleton, which involves synthesis of a starting material having alkyl substituents and the subsequent coupling reaction with a diiodo compound. The inventors of the present invention have suggested that the above problems associated with alkyl groups can be avoided, and have reported that alkyl groups can actually be introduced at the 6- and 13-positions of pentacene (Non-patent Document 5: T. Takahashi, K. Kashima, S. Li, K. Nakajima, K. Kanno “Isolation of 6,13-Dipropylpentacene and its tautomerization” J. Am. Chem. Soc., 129, 2007, pp 15752).